My T gives me the impression that she wouldn't take action for generally anything except a specific intent to act on a specific day, etc.

She knows about my ideations and says that just because I think about it doesn't mean that i'm going to do it and that there is such a wide spectrum of what is considered "suicidal" that she really explores before taking action. So I feel okay in mentioning it to her but it took a lot of reassurance from her (she seemed one step away from annoyed - she finally took the "ok, lets just go ahead and address this head on" approach).

I have told her though, that should I actually be planning to do it I probably wouldn't tell her; in that case she asked if she needed to be concerned about me doing anything.

Now I have told her i'd rather not discuss it at all because I don't want her to not take me seriously if by a tiny tiny tiny chance i'm really feeling suicidal and reach out to her for help (highly unlikely); I don't want her to mix my ideations with the real thing because that would tick me off and drive me to just say "ef it" and do it.

So while I no longer discuss it with her, I don't have to be as cautious about telling her whats on my mind if I desire to do so. She knows i've had impulsive suicidal thoughts without a definite plan and didn't take that any further than to question them for the next few visits. I also let her know that although i'm a "easy" client if she ever tried to "lock me up" (especially if she did so in secret) I would likely react in an extremely uncooperative way.

I think you should be cautious just because everyone reacts a different way and its better to be safe than sorry.